Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A device to detect thermal radiation has a membrane and at least two
detector elements that are respectively set up to transduce thermal
radiation into an electrical signal and are mounted situated next to one
another on the membrane, wherein at least one heat dissipation path is
provided on the side of the membrane facing towards the detector elements
and/or on the side of the membrane facing away from the detector
elements, which heat dissipation path has a higher heat conductivity than
the membrane and is connected with the detector elements in a
heat-conductive manner via the membrane so that heat can be discharged
from the detector elements with the heat dissipation path, whereby the
response time of the detector elements is short; and wherein at least one
heat barrier that has a lower heat conductivity than the membrane and
extends between the detector elements is provided integrated into the
membrane, such that a heat conduction in the membrane from the one
detector element to the other detector element is prevented by the heat
barrier; whereby the crosstalk of the detector elements is low.

Claims:

1.-11. (canceled)

12. A device to detect thermal radiation, comprising:a membrane;at least
two detector elements situated next to each other on said membrane, each
of said at least two detector elements transducing thermal radiation into
an electrical signal;at least one heat dissipation path located at a side
of said membrane, said side of said membrane being selected from the
group consisting of a side of said membrane facing toward said detector
elements and a side of said membrane facing away from said detector
elements;said heat dissipation path having a higher heat conductivity
than said membrane and being in thermal conducting connection with said
membrane to discharge heat via the heat dissipation path from said
detector elements;each of said detector elements having a short response
time; andat least one heat barrier integrated into the membrane, said
heat barrier having a lower heat conductivity than said membrane and
extending between said detector elements to prevent heat conduction
between said detector elements and lower crosstalk between said detector
elements.

13. A device as claimed in claim 12 wherein said heat dissipation path is
comprised of silicon.

14. A device as claimed in claim 13 wherein said heat dissipation path
comprises at least one web in said membrane.

15. A device as claimed in claim 14 wherein said heat dissipation path
comprises a plurality of webs surrounding a region of said membrane in
which at least one of said detector elements is situated.

16. A device as claimed in claim 12 wherein said heat barrier is formed by
an evacuated recess in said membrane.

17. A device as claimed in claim 16 wherein said evacuated recess is
formed as a slit in said membrane proceeding between two of said detector
elements that are adjacent to each other, said slit proceeding
perpendicularly to an imaginary connection line defined by said at least
two detector elements.

18. A device as claimed in claim 17 wherein said slit is a first slit, and
wherein said evacuated recess comprises a second slit proceeding parallel
to said first slit between said at least two detector elements.

19. A device as claimed in claim 18 wherein said heat dissipation path is
located between said first and second slits to thermally insulate said
heat dissipation path from said detector elements except for said
heat-conductive connection.

20. A method to manufacture a device to detect thermal radiation,
comprising the steps of:situating at least two detector elements next to
each other on said membrane, each of said at least two detector elements
transducing thermal radiation into an electrical signal;providing at
least one heat dissipation path at a side of said membrane, said side of
said membrane being selected from the group consisting of a side of said
membrane facing toward said detector elements and a side of said membrane
facing away from said detector elements, said heat dissipation path
having a higher heat conductivity than said membrane, and placing said
heat dissipation path in thermal conducting connection with said membrane
to discharge heat via the heat dissipation path from said detector
elements; andintegrating at least one heat barrier into the membrane,
between said detector elements to prevent heat conduction between said
detector elements and lower crosstalk between said detector elements,
said heat barrier having a lower heat conductivity than said membrane.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The invention concerns a device to detect thermal radiation. In
addition to the device, a method is specified for the production and a
use of the device.

[0003]2. Description of the Prior Art

[0004]A device to detect thermal radiation is known from DE 100 04 216 A1,
for example. This device is designated as a pyrodetector. The detector
element is a pyroelectric detector element. It possesses a layer design
with two electrode layers and a pyroelectric layer with pyroelectrically
sensitive material arranged between the electrode layers. This material
is lead zirconate titanate (PZT). For example, the electrodes consist of
platinum or of a chromium-nickel alloy absorbing the thermal radiation.

[0005]The thermal detector element is connected with a detector element
substrate made of silicon (silicon substrate). An insulation layer for
electrical and thermal insulation of the detector element and the
detector element substrate from one another is arranged between said
detector element and the detector element substrate. The insulation layer
thereby possesses: an evacuated void that extends across a base surface
of the detector element; a support layer of the void; and a cover of the
support layer and the void. The support layer consists of polysilicon.
The cover is made of a boron-phosphorus-silicate glass (BPSG). A readout
circuit is integrated into the detector element substrate to read out,
process and/or relay the electrical signal generated by the detector
element. The readout circuit is realized via the CMOS (Complementary
Metal Oxide Semiconductor) technique.

[0006]A device comparable to this for the detection of thermal radiation
is known from DE 195 25 071 A1. The thermal detector element is likewise
a pyroelectric detector element described above. The detector is arranged
on a multi-layer detector element substrate. One of the layers of the
detector element substrate is an electrically insulating membrane. The
membrane consists of a Si3N4/SiO2/Si3N4 triple
layer, for example. The membrane is in turn applied on a silicon
substrate of the detector element substrate.

[0007]In the known devices a number of detector elements are present
(detector element array). In order to obtain an optimally high spatial
resolution, the detector elements are arranged optimally close to one
another. However, the more closely that the detector elements are
arranged, the higher the probability of a "crosstalk". The desired high
resolution is lost.

SUMMARY OF THE INVENTION

[0008]It is the object of the invention to specify a compact device to
detect thermal radiation, wherein the device has both high spatial
resolution and a low response time.

[0009]To achieve the object, a device to detect thermal radiation is
specified, with a membrane and at least two detector elements that are
respectively set up to transduce thermal radiation into an electrical
signal and are mounted situated next to one another on the membrane,
wherein at least one heat dissipation path is provided on the side of the
membrane facing towards the detector elements and/or on the side of the
membrane facing away from the detector elements, which heat dissipation
path has a higher heat conductivity than the membrane and is connected
with the detector elements in a heat-conductive manner via the membrane
so that heat can be discharged from the detector elements with the heat
dissipation path, whereby the response time of the detector elements is
short; and wherein at least one heat barrier that has a lower heat
conductivity than the membrane and extends between the detector elements
is provided integrated into the membrane, such that a heat conduction in
the membrane from the one detector element to the other detector element
is prevented by the heat barrier; whereby the crosstalk of the detector
elements is low.

[0010]To achieve the object, a method is also specified for the production
of the device with the following method steps: a) provide a membrane with
at least one heat sink in the form of the heat dissipation path to
generate a directed heat flow and at least one thermal regulation device
in the form of the heat barrier to regulate the heat flow and b) arrange
the thermal detector elements on the membrane such that heat flow away
from at least one of the thermal detector elements in the direction of
the heat sink (set up my means of said heat sink) can be generated and a
magnitude of the heat flow can be regulated by the regulation device.

[0011]The device according to the invention can also be used as a movement
sensor, as a presence sensor and/or as a heat image camera according to
the invention.

[0012]The thermal radiation to be detected has a wavelength of over 1
μm. The wavelength is advantageously selected from the range from 5 to
15 μm. The thermal detector element is based on the Seebeck effect,
for example. The thermal detector element is advantageously a
pyroelectric detector element. As described above, the pyroelectric
detector element consists of a pyroelectric layer with a pyroelectrically
sensitive material and electrode layers mounted on both sides. The
pyroelectrically sensitive material is, for example, a ceramic such as
lithium niobate (LiNbO3) or lead zirconate titanate. A ferroelectric
polymer such as polyvinylidene fluoride (PVDF) is also conceivable.
Platinum or a platinum alloy is considered as an electrode material of
the electrode layers, for example. A chromium-nickel electrode or an
electrode made from an electrically conductive oxide is also conceivable.
For example, a detector element possesses a rectangular footprint with an
edge length of 10 μm to 200 μm. Smaller edge lengths (for example 5
μm) or even greater edge lengths of up to 400 μm are likewise
conceivable. An element center-to-center spacing (pitch) amounts to 20
μm to 400 μm. Larger spacings are also conceivable.

[0013]The heat sink in the form of the heat dissipation path leads to the
generation of the heat flow, and therefore to a transportation of heat
away from the detector elements. The heat sink and the detector elements
are connected with one another in a thermally conductive manner. Without
additional measures, however, a sensitivity of the detector elements
would be markedly reduced via an increased heat flow that is entailed by
this. As a countermeasure the regulation device is present in the form of
the heat barrier. The dimension (magnitude) of the heat flow is adjusted
with the aid of the regulation device. The regulation device acts as a
thermal resistor. It is thereby achieved that the sensitivity of the
detector elements is maintained.

[0014]The detector element and the additional detector element are
arranged next to one another on a surface segment of a common detector
element substrate that is formed by the membrane. The detector elements
can be arranged very close to one another in that the thermal crosstalk
or, respectively, the thermal coupling between the detector elements is
efficiently suppressed.

[0015]The heat sink is arranged between the thermal detector element and
the additional thermal detector element. In this configuration the heat
emitted by the detector element and the additional adjacent detector
element is dissipated. There is no thermal crosstalk between the detector
elements.

[0016]The heat sink is advantageously arranged on the surface segment on
which the detector elements are arranged. As an alternative to thus, the
heat sink is arranged on a side of the detector element substrate facing
away from the surface segment. The heat sink is arranged on the back side
of the detector element substrate. It is also conceivable that the heat
sink is arranged on both sides, thus on the detector element side or
[sic] on the reverse side of the detector element substrate.

[0017]The heat dissipation path is preferably made of silicon. The common
detector element substrate possesses the membrane that forms the surface
segment on which the detector elements are arranged. The membrane
consists of a membrane layer or of multiple membrane layers. A plurality
of inorganic or organic materials can thereby be used. For example, the
membrane layer is made of silicon dioxide (SiO2) or silicon nitride
(Si3N4). The particular advantage of layers made of these
materials is the electrical and thermal insulation effect of the
materials. These materials act as electrical and thermal insulators.

[0018]The heat dissipation path is preferably fashioned as a web that is
arranged on the membrane. It is also preferable that the heat dissipation
path is formed by a plurality of the webs that surround a region of the
membrane in which at least one of the detector elements is arranged. The
heat sink and/or the regulation device are respectively a component of
the common detector element substrate. This in particular is achieved in
that the heat sink possesses at least one web with thermally conductive
material that is arranged on the common detector element substrate. The
web or the webs can be arranged on the front side and on the back side.
The heat is efficiently discharged in the direction of the heat sink via
the webs. The webs additionally fulfill a support function: this is in
particular advantageous with regard to the manufacturing of the device
with wafer bond processes.

[0019]Alternatively, the heat dissipation path is preferably formed by a
thin film that is arranged on the membrane. The heat sink is thus
preferably the thin film with thermally conductive material that is
applied on the detector element substrate. The detector element substrate
is, for example, a multilayer membrane (mentioned above). In this
multilayer membrane a layer can be integrated as a material that has good
thermal conductivity. The heat is dissipated in a directed manner via
this layer, which is in turn connected in a thermally conductive manner
with a heat sink. Arbitrary materials are conceivable as a thermally
conductive material of the web or a thin film. The thermally conductive
material is advantageously silicon, as it is preferably used in CMOS
technology.

[0020]The heat barrier is preferably an evacuated recess provided in the
membrane. The regulation device thus preferably possesses a clearance of
the detector element substrate. For example, a thinning of the detector
element substrate or a hole in the detector element substrate is
conceivable. A thermal cross section of the detector element substrate is
reduced by the recess in comparison to a detector element substrate
without recess. This leads to a reduction of a lateral heat transfer.
This leads to the situation that the heat flow from a detector element to
the heat sink is hindered. As a consequence of this the sensitivity of
the detector element or, respectively, of the detector elements is
maintained to the greatest possible extent.

[0021]The evacuated recess is preferably a slit provided in the membrane
that runs between two adjacent detector elements, perpendicular to an
imaginary connection line defined by the two detector elements. It is
preferred that at least two slits parallel to one another and running at
the same level are provided so that the slits are arranged between the
detector elements. Moreover, it is preferred that the heat dissipation
path runs between the slits so that the heat dissipation path is
thermally insulated from the detector elements by the slits.

[0022]The detector elements are attached to the membrane and are in
heat-conductive contact with it. Therefore the detector elements are
coupled in a heat-conductive manner with one another via the membrane.
The heat conduction through the membrane from the one detector element to
the other detector element is defined by the heat conductivity
coefficients of the membrane and the membrane thickness. In that the heat
barrier is arranged between the detector elements, the detector elements
are thermally insulated from one another by the membrane with regard to
their heat exchange. A crosstalk of the detector elements due to the heat
exchange is thereby reduced. The spatial resolution of the device is thus
high although the population density of the membrane with the detector
elements is high. The detector element is also rapidly heated by the
thermal radiation since, due to the insulation effect of the heat
barrier, only small amounts of heat are dissipated from the detector
element through the membrane. The rise of the electrical signal at the
point in time of the incidence of the thermal radiation on the detector
element is therefore steep. However, it is hereby disadvantageous that,
due to the insulation effect of the heat barrier, the detector element
only cools slowly via heat dissipation across the membrane at the end of
the heat radiation. This would have the consequence that the response
time of the detector element would be long. The provision of the heat
dissipation path with which heat is quickly discharged from the detector
element provides relief so that--due to the heat dissipation effect of
the heat dissipation path--the detector element cools rapidly via heat
dissipation over the heat dissipation path at the end of the heat
radiation. The drop-off of the electrical signal at the point in time of
the absence of the thermal radiation at the detector element is thereby
steep. The response time of the device is thus short, although the device
has a high population density with the detectors.

[0023]According to the further aspect of the invention, the device is used
as a movement sensor, as a presence sensor and/or as a heat image camera.
For the heat image camera the device is equipped with a plurality of
detector elements, for example 240×320 detector elements (QVGA
standard) or more. This is possible due to the high integration density
(number of detector elements per areal unit).

[0024]In summary, the following advantages of the invention are to be
emphasized: [0025]The device for detection of thermal radiation is
compact. [0026]An increased integration density in comparison to the
prior art is [sic] via the invention. [0027]A crosstalk probability
between adjacent detector elements is reduced. At the same time, however,
the sensitivity of the individual detector elements is maintained
[0028]The device is in particular mechanically stabilized given the use
of webs.

[0029]The device for detection of thermal radiation is presented in the
following using an exemplary embodiment and associated Figures. Figures
are schematic and do not show any illustrations to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1A shows a device for detection of thermal radiation in
accordance with the present invention, in a perspective view from above.

[0031]FIG. 1B shows the device for detection of thermal radiation of FIG.
1A in a perspective view from below.

[0032]FIG. 2 is a lateral cross-section through a detector element on a
detector element substrate in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033]The device 1 for detection of thermal radiation possesses a detector
element substrate 10 with a membrane 101 on which are mounted a thermal
detector element 11 and at least one additional thermal detector element
12. The detector element substrate possesses a silicon substrate 100. The
thermal detector elements are arranged in a detector element array 110 on
the surface segment 102 of the membrane. A detector element array with
2×2 detector elements is shown as an example in FIG. 1A.

[0034]The detector elements 11 and 12 are pyroelectric detector elements
in thin film design with two electrode layers 112 and 122 and a
pyroelectric layer 113 and 123 respectively arranged between the
electrode layers (FIG. 2). The pyroelectric layer is respectively a layer
made of PZT as a pyroelectrically sensitive material, approximately 1
μm thick. The electrode layers are made of platinum and a
chromium-nickel alloy with layer thicknesses of approximately 20 nm,

[0035]The membrane 101 is a Si3N4/SiO2/Si3N4
triple layer. For the detector elements, a readout circuit (not shown) is
integrated into the silicon substrate of the detector element substrate.

[0036]Thin webs 104 made of silicon are arranged between the detector
elements, both on the front side 102 and on the back side 103. The thin
webs act as respective heat sinks from at least one of the detector
elements away to a heat sink. The heat sink is now shown.

[0037]Moreover, clearances in the form of slits 105 are contained in the
membrane. The slits act as regulation devices to regulate the respective
heat flow.

[0038]Finite element (FEM) simulations of the thermal overcoupling in the
example of detector elements with a base area of 200×200
μm2 given a pitch of the detector elements of 400 μm have
confirmed the effectiveness of the inventive combination of slit and web:

[0039]Production of the device proceeds as follows: a) provide detector
element substrate with a surface segment, at least one heat sink to
generate a directed heat flow and at least one thermal regulation device
to regulate the heat flow and b) arrange the thermal detector elements on
the surface segment of the detector element substrate such that a
directed heat flow directed away from at least one of the thermal
detector elements is generated by means of the heat sink in the direction
of said heat sink, and a magnitude of the heat flow can be regulated by
means of the regulation device. The detector elements are mounted on the
surface segment of the prefabricated detector element substrate. As an
alternative to this, a detector element substrate is initially provided
with the webs. The introduction of the slits (regulation device) ensues
after the arrangement of the detector elements. The arrangement of the
detector elements ensues in a typical manner, for example via sputtering
of the individual layers.

[0040]After the arrangement what is known as a back-side etching is
implemented. Material of the silicon substrate is removed from the back
side, thus the side of the silicon substrate that is facing away from the
detector elements. The slits are thereby uncovered.

[0041]The device is used in a movement sensor, a presence sensor or a heat
image camera.

[0042]Although modifications and changes may be suggested by those skilled
in the art, it is the intention of the inventors to embody within the
patent warranted heron all changes and modifications as reasonably and
properly come within the scope of their contribution to the art.

Patent applications by Carsten Giebeler, Edinburgh GB

Patent applications by Matthias Schreiter, Munich DE

Patent applications in class With temperature modifying means

Patent applications in all subclasses With temperature modifying means